We are studying the control of cell division in S. cerevisiae. The pathway of events in the cell division cycle is being defined with inhibitors and temperature sensitive mutants. The step within this pathway where division is controlled in response to nutritional deprivation or arrest by mating factors has been identified as that controlled by gene cdc 28. Selection procedures for cdc 28-like mutants have been devised and will be exploited to further define this step. The mechanism of mating factor arrest at this step will be investigated utilizing genetic as well biochemical techniques. Finally the coordination of growth and division which also occurs at the cdc 28 mediated step will be studied by isolating mutants with altered size control. This work should lead to an identification of the genes that control division and some insight into the role that each gene product plays in this process.